Ophthalmic laser treatment devices are nowadays used in many places for the correction of refractive errors, as well as other eye diseases. In this case, structures are produced in an eye tissue, and can subsequently be extracted, or incisions are made which correct a refractive error by a relaxing effect of the cornea. Detachment symptoms can be corrected. Very often, ophthalmic laser treatment devices are used for cataract surgery, in which the clouded lens of a patient's eye is removed and an intra-ocular lens (IOL) is inserted in its place.
Incision figures generated by a treatment laser beam, by use of photodisruption, are the most frequent applications of an ophthalmic laser treatment device. However, using a treatment laser beam, structures can also be produced by an ablation effect, or otherwise structured tissue changes or tissue adhesions can be produced by a coagulation effect.
During the process of introducing a structure into an eye tissue with a treatment laser beam for example an incision figure made in the cornea, the sclera or the lens and its lens capsule the target can move away from the initial position due to eye movements. The resulting structure then deviates from the planned structure, and is a superimposition of the movement of the focus of the treatment laser beam along a scanning pattern which encodes this structure with the unintended movement of the patient's eye which is being treated.
If at this point, the generation of this structure, in particular an incision figure and/or incision line, begins at a starting point, and the ending point of the generation of the structure by use of the focused treatment laser beam should coincide with this starting point so that a closed structure separates an enclosed volume or an enclosed surface, the result of a movement of the patient's eye being treated is that the starting point and the ending point of the structure no longer meet. If the beginning and the end of an original incision figure no longer meet in a tissue of a patient's eye, the volume within this incision figure is no longer completely separated from the tissue located outside the incision figure. This can be a problem in keratoplasty operations in the cornea, and more particularly in the execution of a capsulotomy incision in cataract operations.
In the case of multi-path incisions, for example, the intended lateral incision figure—that is, the incision figure as can be seen in a top view, is repeated several times successively at slightly varying depths in the target object. In this way, on the one hand, the depth expansion of the target object is covered, a continuous cut is made possible as a result, and deviations in the target object depth and of the cutting depth which are due to tolerances are also bridged. Since different depths of the target object can be produced with different parts of the successively repeated incision figure, if the target object moves, unconnected pieces of the sectioned surface and/or multiple executions of the incision result, because the incision figure is then slightly offset laterally rather than exactly repeated.
FIG. 1A illustrates such a situation in the context of multipath incisions according to the prior art. The sectioned area of the incision FIG. 1 penetrates the incision area 20 along a spatial path. If the sectioned area is composed of incision lines 11 repeated multiple times with a slight vertical offset, or has a helix-like structure, each incision line penetrates the incision area 20 at a vertical height only in a subsector 12 near to the spatial penetration path, and thus effects an incision action there. If, during the incision, there is an offset of the sectioned area, the subsectors 12 have an offset to one another.
FIG. 1B shows various possibilities for the offset of the incision lines in a top view AO of the sectioned area of the incision FIG. 1, and the resulting incision lines of the incision area 20 during the execution of the incision, with lateral offset to the extent of vector u as in the respective figures (i), (ii), (iii). Between the individual subsectors 12, there are gaps as well as overlap, depending on the direction of the offset. The offset positions when a structure is generated in a tissue of a patient's eye are not known a priori.
In the case of single-path incisions according to the prior art, the intended incision FIG. 1 is produced by a single slow sweep and/or “traverse” of a line which is visible in a top view of the incision FIG. 1, rapidly sweeping over a surface which is inclined with respect to the projection surface of the view most commonly a surface perpendicular to the projection surface along this line. In the prior art, the projection surface corresponds to the lateral plane that is, to a plane perpendicular to the optical axis and the incision figure is executed by rapidly sweeping over a depth range during a slow sweep of the line visible in the top view. As shown in FIG. 2A, the sectioned area of the incision FIG. 1 is constructed from adjacent vertical straight lines 13 along an (incisional) line. In this case, the closed incision figure should be circular in the top view. The straight lines 13 penetrate the incision area 20 only in will partial height sections 14, producing an incision effect in these locations.
Adjacent straight lines 13 are also executed in short time intervals, and therefore have only a small offset if there is a temporally variable offset of the sectioned area 20 during the incision relative to the preceding straight line 13. It is only when the end of the incision line needs to once more meet with the beginning that a total offset that is, the offset which arises between the beginning and the completion of the production of the incision FIG. 1 is noticeable.
Without further measures, therefore, the beginning and end of the incision figure would not coincide if the patient's eye moves, nor if there are movements due to other influences during the use of the ophthalmic laser treatment device. The incision would be incomplete.
FIG. 2B shows a top view AO of such an originally circular incision FIG. 1 as is used, for example, for a capsulotomy of the eye lens. It begins at a starting point 2 and ends at the ending point 3. If the sectioned object does not move during the duration of the incision, a closed incision FIG. 1 results. However, if the object moves during the duration of the incision by the vector u, non-closed incision figures can also occur according to the direction of movement and the inner circular part thereof cannot be removed as intended.